1. Field of the Invention
The present invention relates generally to charge pump circuits, and in particular to charge pump circuits that provide a regulated output voltage.
2. Discussion of the Related Art
A charge pump circuit is generally used for boosting a power supply voltage to a higher voltage level to be used for powering ancillary circuits. Closed loop control is sometimes used with charge pumps to provide a regulated output voltage. However, charge pumps that include closed loop control typically have extremely slow response times due to the relatively small amount of energy that can be transferred during each clock cycle. Exacerbating the slow response times is the effect of inherent leakage currents that occur within the charge pump. When diodes within the charge pump are back biased, a small but significant leakage current flows backwards through the diode. Leakage currents transfer charge out of the output storage devices back to the voltage supply, causing the charge pump output voltage to decrease until the next cycle begins. The loading effect of leakage currents on the charge pump output voltage causes an undesirable increase in the ripple amplitude of the output voltage. Compensating for the effect of leakage currents is problematic, since the magnitude of leakage currents is dependent on several factors including the semiconductor manufacturing process, die defects, and temperature.
The present invention provides a circuit and method for generating a regulated voltage from a first voltage of a first voltage source. The regulator circuit includes at least two boost circuits. A first boost circuit generates a first pump voltage. The first boost circuit includes a charge pump for generating the first pump voltage from a first voltage source. The charge pump includes a charge pump switch having a leakage current. A second boost circuit generates a second pump voltage. The second boost circuit includes a charge pump for generating the second pump voltage from a second voltage source. A compensation circuit coupled between the first boost circuit and the second boost circuit supplies a compensation current to the first boost circuit to compensate for energy losses caused by the first boost circuit leakage current. An amplifier includes a reference input coupled to a reference voltage, and a sense input coupled to a sense signal representative of the first pump voltage. The amplifier is operable in response to a difference between the reference voltage and the sense signal, to control the first boost circuit output.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.